This invention relates generally to the precise alignment of beams and, more specifically to devices for the precise alignment of particle accelerators, lasers, optical systems, or other beam producing apparatus.
Beam producing apparatus, such as particle accelerators, lasers, optical systems and the like, often is connected to an associated structure, which may contain an assembly of such things as lenses, collimators, beam splitters magnets, or any other equipment intended to control, direct, or otherwise modify the beam. Precise alignment of this associated structure is essential if the beam producing apparatus is to perform its intended function.
Although initial alignment of the structure may be readily accomplished manually with removable targets, maintaining this alignment over an extended period of operation can be difficult, depending upon the environment in which the beam apparatus is deployed. Pressure, temperature, radiation, or other environmental changes during operation can adversely affect the structural members associated with the beam producing apparatus, causing misalignment of the path of the beam.
When beam producing devices are employed in a laboratory, or a manned, ground location, realignment to correct any deviation of the structure can normally be easily accomplished by either mechanical or manual means. Actually, because environmental conditions in these settings are often controlled, realignment is not often necessary. However, beam producing devices are being deployed in increasing numbers in more hostile environments, such as at remote earth locations and in space. In these more hostile locations, which may even be unmanned manual realignment may not be possible, although frequent readjustment of the associated structure may be required because of the particular nature of the environment. These locations dictate the use of automatic alignment systems to maintain the beam producing device in proper alignment during and after an environmental perturbation.
Various types of automatic alignment systems have been used in the past, many utilizing sensors to control movement of the mirrors which directed the beam. In some cases, these sensors were quad-cell detectors placed in the path of an adjacent laser beam to detect misalignment. However, as quad-cell detectors necessarily intercept this beam, causing high energy losses, they cannot be directly employed in a series configuration to control multiple sections of a beam directing structure. Therefore, any such use must be carefully engineered.
In some applications it may be possible to mechanically insert a quad-cell detector temporarily into the path of the beam to determine its alignment. However, precise alignment requires that the detector be accurately located at exactly the same location with respect to the surrounding structure upon each insertion. Such accuracy is difficult to attain even in manned, ground locations, and is essentially impossible in the environment of space. Mechanical placement of sensors in the path of the main beam is therefore not an acceptable design choice.
Quad-cell detectors are, however, useful devices when properly utilized. These devices contain an array of photodetecting material deposited on a substrate in four separated quadrants. The electrical output from each quadrant is proportionate to the quantity of light energy incident to its surface. When the light is striking the central area of the surface, all four outputs are equal. This electrical output is connected to differential amplifiers which can in turn operate electromechanical positioning devices. Quad-cell detectors are generally commercially available.
In use, should the light move from the central area of the detector, the quadrant or quadrants receiving the light would produce a voltage signal proportional to the energy incident to each quadrant which, when used in conjunction with a differential amplifier, can effect realignment of the beam or its associated structure. However, as previously stated, care must be taken in their use because quad-cell detectors intercept the laser beam.
A method of alignment of a high power laser is disclosed in U.S. Pat. No. 4,146,329 to King, et al. This alignment system utilizes a separate reference laser which propagates coaxially with an annular main laser beam until it is extracted. This extracted reference beam acts as an incident beam to a null position sensor, such as a quad-cell detector. The quad-cell generates an electrical error signal should the reference beam move from the null position. This error signal is used by servo-electronics to reposition a mirror until realignment is achieved.
As explained in the patent, the HeNe reference laser must be securely affixed to the bench supporting the main laser, and should be enclosed in a temperature controlled environment to maintain the stability necessary for this application. These requirements would be very difficult to achieve in a hostile environment.
An automatic alignment system using detectors in the path of a main laser beam is disclosed in U.S. Pat. No. 4,675,501 to Klingel. In this case, the detectors have a central aperture through which the main beam passes when properly in alignment. Mirrors used to direct the main beam are angularly repositioned in response to electrical signals from the detectors when a portion of the beam strikes the detector surrounding the aperture, indicating misalignment. A serious problem with this configuration, as stated in the patent, is that the detectors could be damaged by a major misalignment of the beam.
Neither of these patents provide any teachings of apparatus or method for maintaining the alignment of beam modifying structures. The prior art provides little guidance for accomplishing this function, although the deployment of beam producing apparatus utilizing associated structures is on the increase.
It is therefore an object of the present invention to provide apparatus for precisely maintaining the alignment of beams through control of the associated structure.
It is a further object of the present invention to provide a system for aligning beams which operates automatically.
It is a still further object of the invention to provide system capable of controlling a structure having multiple segments.
It is a still further object of the invention to provide an automatic alignment system which will operate reliably in an environment hostile to the maintenance of alignment of the structure associated with a main beam.
It is a still further object of the present invention to provide an automatic beam alignment system employing a series plurality of reference beam detecting stations without introducing significant losses of the reference beam.